Here's a classic trick for beginners, a variation on the cut and restored plot , which involves shearing a string in half as it resides in a straw and then restoring the string so it's whole again. Even though the string is inside the straw and you've cut the straw in half, the string is somehow untouched.
This one is easy and quite baffling.
string that is slightly longer than the drinking straw (I'm using purple dental floss in the pictures for visibility)
A plastic drinking straw
Repeatedly bend the straw in its middle until there’s a crack in the center of the straw. The opening in the center of the straw is the secret to the trick.